The present invention relates to a method and a system for controlling quality of service over a network, and in particularxe2x80x94over a packet switched data network, such as over IP (Internet Protocol).
It is widely known, that modem telecommunication networks comprise different interconnected domains, for example a PSTN (Public Switched Telephone Network) which was originally designed for handling voice calls, and a packet switched network which, by its nature, is data oriented. Nowadays, all kinds of services or transmission types (e.g., voice, fax or data) are transmitted through the combined networks and are inevitably subjected to many factors which affect the quality of service expected by a particular subscriber. The above-mentioned factors stem not only from the nature of a particular network domain, but also (and to the great extent) from the growing traffic load in the modem telecommunication networks.
In packet switched networks, real time services such as voice, fax, real-time video conference (e.g., packetized voice signals of Voice over IP), are mixed with data signals and, as a result, suffer from degradation that is not encountered in the regular circuit-switched networks (e.g., PSTN). The degradation may occur due to such known packet networks"" problems, as packet loss, packet delay and packet delay variation (so-called jitter) which are known as specific criteria of data transmission quality.
While in the PSTN the voice channels are assigned to a constant, assured bandwidth, in packet switched networks the bandwidth varies dynamically, depending on data and voice traffic in the network. In order to ensure a given quality of the voice signal, a service provider in the packet switched network must assure both a minimum bandwidth at all times, and keep the three criteria mentioned above within given limits. For example, it becomes difficult to carry on a voice conversation if the packet delay exceeds 200 ms.
While for data traffic control in the packet switched networks it may be enough to monitor some performance criteria such as the packet delay, in the case of voice traffic various parameters combine in an infinite number of possible combinations so that, there is no simple correlation between these parameters and the actual voice quality heard by the caller.
Voice networks have traditionally been tested by injection of test sentences at one (transmitting) end, and having this sentence heard and its clarity subjectively graded by a group of people at the other (receiving) end of the path. The test result is called a Mean Opinion Score (MOS) and ranges from 1 (poor) to 5 (excellent).
To convert this obviously subjective method to an objective one, real measurements of quality should serve the basis for conclusions. To this end, two main approaches were proposed. The first one can be classified as an intrusive approach, which is based on comparison of a transmitted signal to the same received signal, and examining the difference. There are a number of models enabling to arrive to the MOS results using the above comparison, for example PSQM model (described in the International ITUT standard Q862) and PAMS model developed by British Telecom (BT). It should be noted, that PAMS is the only model which takes into account problems in the quality of service which may be brought to data networks by phenomena such as packet delay, packet loss, jitter, etc. The second approach is a non-intrusive approach based on measuring physical parameters such as noise, delay, echo etc., and improving thereof up to a satisfactory level. A number of models exist, for example E-model of ITUT standard body and a CCI (Call Clarity Index) developed in BT. Presently, there is no such a non-intrusive model, which would take into account problems of quality degradation due to data networks.
Nowadays, voice services providers which utilize packet switching in their networks, cannot assure the desired voice quality to their customers in advance, since the voice quality of service is not monitored in the networks to the extent allowing that.
On the other hand, fully loaded networks suffer from shortage of lines, and very often the quality of service (with respect to voice, fax and data) is reduced due to low connectivity in the network and low availability of destination points.
None of the relevant methods and systems known to the Applicant describes or suggests any combined Quality of Service estimation mechanism for a network, which would enable integral monitoring of the quality of service, and control of the quality of service to be provided.
It is therefore the object of the present invention to provide a method of determining quality of the telecommunication service over a telecommunication network based on a novel, combined estimation of quality of service for this network. A further object of the invention is to provide a method, a system and an equipment for monitoring and controlling the quality of service in the network, based on the combined estimation thereof. The invention is most effectively applicable to modem telecommunication networks including packet switched networks.
The above main object can be achieved by a method of determining quality of telecommunication service over a telecommunication network, the method including the following steps:
a) obtaining data on quality of service over a number of routes in the network by determining, for each route, N of parameters pi, each of said parameters pi reflecting either a quality of transmission of a particular service (transmission type) through said route or a statistical characteristics of said route""s availability to a subscriber,
b) building an objective quality score (OQS) for each of said routes, the OQS being a multi-profile quality estimation equation presenting a sum of N said parameters pi taken with respective weight functions Wi(pi) thereof.
It is further proposed, that the weight functions Wi(pi) reflect a preferred profile of the quality of service in said network and are presented as positive numbers in the range 0xe2x89xa6Wi(pi)xe2x89xa61 selected so that M values of said weight functions Wi(pi) are more than 0, (Mxe2x89xa6N), and the sum of the selected values of the Wi(pi) is equal to 1.
Preferably, the method also comprises step (c):
c) selecting one or more routes having the OQS value not lower than a predetermined OQS value for further routing the telecommunication services there-through.
It should be mentioned, that for effecting control of the service quality, an additional step is to be effected, i.e. the step of routing the telecommunication services over said one or more selected routes.
It is understood, that said particular service (transmission type) is one of components in a non-limiting list comprising voice, fax and data.
The mentioned equation can be presented in the following form:                     OQS        =                              ∑                          i              =              1                        N                    ⁢                                                    W                i                            ⁡                              (                                  p                  i                                )                                      ⁢                          p              i                                                  1      
wherein:
OQSxe2x80x94is the objective quality score estimation
pixe2x80x94a value of a parameter xe2x80x9cixe2x80x9d in a particular route in the network
Wi(pi)xe2x80x94weight function of the parameter xe2x80x9cixe2x80x9d (in one simple particular case Wi(pi) may be a constant coefficient of the parameter xe2x80x9cixe2x80x9d)
Nxe2x80x94is the number of parameters defined for the network.
The above-mentioned parameters preferably comprise at least the following five (N=6) characteristics of the quality of service for particular transmission types and the network of interest:
p1xe2x80x94is a voice Quality of Service parameter QoS which can be estimated using at least one of the following methods known in the prior art: CCI (Call Clarity Index), PAMS (Perceptual Analysis Measurement System), PSQM (as defined in the international ITUT standard Q-862), E-model, etc.,
P2xe2x80x94is a Fax Quality of Service parameter estimated, for example, according to a statistically obtained ratio between a number of errors during a fax transmission and a number of pages in the fax, or other methods, for example based on checking a coded message enclosed in a particular fax packet.
P3xe2x80x94is a Data Quality of Service parameter which can be estimated based on such a widely known transmission parameters as Packet delay, Packet loss and Packet delay variation (jitter);
P4xe2x80x94is Line Availability in the network, which parameter can be calculated using statistical parameters of physical reliability of a line, i.e., MTBF (MeanTime Between Failure) and MTTR (MeanTime to Repair);
P5xe2x80x94is Connectivity of the network which may be obtained from statistically calculated parameters ASR (Answer Seizure Ratio) and NER (Network Effectiveness Ratio) estimating a number of successful calls with respect to a number of the initiated calls, and calls provided by the destination network portion, respectively;
P6xe2x80x94is a Service Availability parameter, statistically reflecting ratio is of the responses xe2x80x9cbusyxe2x80x9d or xe2x80x9cnot availablexe2x80x9d to the inquiry calls, with respect to the requested destination numbers or sites.
In one version of the method, the weight functions Wi(pi) of the quality of service can be selected by a service provider for forming a number of profiles of services to be offered to clients.
The mentioned pair of a service provider and a client may reflect various combinations, for example a service provider and a particular customer (subscriber); two service providers being inter-carriers; a service provider and a xe2x80x9cclearing housexe2x80x9d; a clearing house and a network provider and the like.
In another possible version, the weight functions Wi(pi) of the quality of service can be selected by a client in order to form its own profile of service. The client uses the weight functions for estimating various options of the service profile and further choosing the most reasonable one.
In both mentioned versions a so-called service level agreement (SLA) can be signed (accepted) between the service provider and the client, which agreement comprises both the selected weights and the selected OQS parameter.
In practice, the client selects the mentioned M parameters with the weight functions thereof (i.e., the parameters which are important for the services of interest), thereby selecting the preferred profile of service. The service provider estimates OQS for a variety of routes using the profile of service obtained from the subscriber, for proposing variants of the xe2x80x9ctotalxe2x80x9d quality to the subscriber. The subscriber is then invited to select a preferred OQS value(s). Upon doing that, the service provider accepts its obligation to route all the services of this particular subscriber along those routes which have been found to satisfy the required total quality of service OQS.
It should be appreciated that the above method may terminate with a step (d) of routing the services over one or more routes which have been selected at step (c).
However, the method may further comprise a step (e) of monitoring the quality of service in real time and comparing it with the predetermined value OQS.
Preferably, the step (e) comprises obtaining data on quality of service over a particular selected route in the network by determining M of said parameters pi and building an objective quality score (OQS) for said route, the OQS being a multi-profile quality estimation equation presenting a sum of M said parameters pi taken with said weight functions Wi(pi).
Those skilled in the art understand that in such telecommunication networks as PSTN and ATM the routing is accomplished in a fixed way. It means, that if the routes selected at step (c) are then found to supply the quality of service lower than was expected, the situation can be improved only physically, for example by effecting repairs in the network. In other words, the monitoring allows for obtaining the updated information about channels"" quality which might be useful for the purposes of the equipment maintenance and improvement of the service.
It is known, that for IP domains the situation is different, i.e. the routing is more flexible. In view of this, the method may comprise a feedback feature, i.e.
step (e) additionally comprises real-time monitoring the OQS of a plurality of routes in the network, and a step of near real-time re-routing the telecommunication services to those routes which are characterized by OQS value not lower than the predetermined value; the re-routing is provided in case that the selected route has the OQS lower than the predetermined value.
For example, the real-time monitoring the OQS of a plurality of routes in the network with respect to a particular transmission type may be provided in the following way:
obtaining data on quality of service concerning said particular transmission type from a plurality of points in the network, distributed therein,
processing the obtained data to determine a corresponding current value of pi parameter for said plurality of points, and
defining in said network a number of alternative transmission paths for said transmission type, each having a particular current value of the parameter pi.
In one particular version of the method, said parameter pi is the Voice Quality of Service parameter QoS, and said network comprises a packet switched network such as IP network.
It should be noted that more than one pi can be determined and monitored according to the above version. The re-routing of the particular transmission type signal can be thus effected via those of said transmission paths having current values of said at least one pi parameter being not lower than said selected Wi(pi)pi.
The method comprising feedback enables the service provider to fulfill the obligations according to the Service Level Agreement (SLA) proposed to a customer by assuring a desired end-to-end quality of service in the network.
Further, the method may include a step of quality related call billing, where a call is billed taking into account the quality actually delivered or preliminarily ordered. It is natural that any combination of the parameter pi with its weight function Wi(pi) having values from 0 to 1 can be associated with an appropriate price function. Based on this, the OQS estimation can be reflected by a specific price range offered by the service provider. Similarly, the SLA signed between the service provider and the subscriber reflects not only the profile of service the subscriber has selected, but also the prices associated with this profile. Alternatively or in addition to the SLA, the caller may indicate the level of quality/cost desired in real time (for example, for an international voice call he/she may request a higher QoS than for a national long distance call).
The method would enable the service providers to offer voice, fax and data transmission services of various quality ranges and at appropriate prices, beginning from full price high quality services up to premium services.
According to a second aspect of the present invention, there is also provided a system for determining and monitoring quality of service in a telecommunication network.
The system for determining a quality of service estimate in a network may comprise:
a plurality of test units capable of collecting data for determining value of at least one quality of service parameter pi with respect to a particular transmission type at various points in said network, said parameter pi being one of N quality of service parameters;
a server computer adapted to communicate with said test units for receiving therefrom the collected data on said at least one parameter at said respective points of the network, said server computer being capable of defining a number of transmission paths (routes) in the network, each having its own said quality of service parameter pi.
Preferably, the server computer is adapted to communicate with the test units collecting data on at least one additional quality of service parameter of said N quality of service parameters, and, based on the collected data concerning the points and the parameters, the server computer being capable of building an objective quality score (OQS) for a number of routes in the network, wherein the OQS is a multi-profile quality estimation equation presenting a sum of N said parameters pi taken with respective weight functions Wi(pi) thereof.
According to the preferred embodiment of the system, said plurality of test units are also capable of monitoring said at least one parameter pi in real time, while said server computer adapted to define in real time a number of transmission paths each having its own current value of quality of service parameter pi.
In one particular embodiment of the system, where the voice QoS parameter pi is monitored, it enables the service provider to measure the audio quality of individual packetized voice channels (voice transmission paths) xe2x80x9cburiedxe2x80x9d in a data communications traffic.
Preferably, the server computer is also capable of ranking said paths according to their pi parameter. Such an ability can be used for various purposes, for example: for reporting on poor quality of particular channels, for further routing a particular transmission type incoming the packet network, and/or for assigning different tariffs to the paths with different ranks of pi.
According to one exemplary embodiment of the system, wherein the packet switched network cooperates with a gateway circuitry where an analog voice signal is packetized and routed, the above-mentioned gateway circuitry comprises a service provider""s network element responsible for routing said voice signals, and the server computer is capable of providing said element with information on the defined transmission paths and respective values of their voice quality of service pi(QoS) parameter, thereby enabling the routing of the voice signals via those of said transmission paths having predetermined values of the QoS parameter. Actually, in this embodiment the system for monitoring becomes a system for providing improved voice service in a packet switched network.
The mentioned service provider""s network element where the analog voice signal is packetized and routed (as well as the element where the packetized voice signal is de-packetized and passed to its destination) may constitute a Voice over IP (VoIP) gateway or gatekeeper.
The above-mentioned server computer, and an equipment kit including at least one such server computer and, optionally, a number of the described test unitsxe2x80x94form additional aspects of the present invention.
For example, a server computer can be designed for determining a quality of service in a network, the server computer being designed for communicating with a plurality of test units for receiving therefrom data on quality of service parameters pi at various points of the network; based on the collected data concerning the points and the parameters, the server computer being capable of building an objective quality score (OQS) for a number of routes in the network, wherein the OQS being a multi-profile quality estimation equation presenting a sum of said parameters pi taken with respective weight functions Wi(pi) thereof., wherein
each of said test units being adapted to determine value of at least one quality of service parameter pi with respect to a particular transmission type.
The service computer can definitely be used for monitoring the quality of service, and for routing in the network based on the OQS estimation.
Further features of the system will become apparent from the following description of the preferred embodiments.